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Working principle of thermal relay
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Author:cnliket
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Published time: 2020-05-21
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The over-current element is composed of bimetallic sheet. The principle of thermal relay is that when the current is too large, the bimetallic sheet heats up, so that it deforms and displaces, and the protective contact is opened, and the contactor control circuit is disconnected, so that the main circuit is powered off After the temperature is lowered, the bimetallic plate cools, and the circuit is restored, but the self-protection control loop of the main circuit has been disconnected, and it needs to be restarted to restart the work. The thermal relay is used for overloading of motors or other electrical equipment and electrical circuits. Protective electrical appliances for protection.
The working principle of the thermal relay in the motor: In the actual operation of the motor, such as when the production machinery is dragged to work, if the machinery is abnormal or the circuit is abnormal, the motor encounters an overload, the motor speed decreases and the current in the winding will increase Large, so that the winding temperature of the motor increases. If the overload current is not large and the overload time is short, the motor winding does not exceed the allowable temperature rise, this overload is allowed. However, if the overload time is long and the overload current is large, the temperature rise of the motor winding will exceed the allowable value, aging the motor winding, shortening the service life of the motor, and even burning the motor winding in severe cases. Therefore, this type of overload cannot be sustained by the motor. The thermal relay is the use of the thermal effect principle of current to cut off the motor circuit when there is an overload that the motor cannot withstand, and provides a protective electrical appliance for the motor to protect against overload.
The working principle of the thermal relay in the motor: When the thermal relay is used for overload protection of the motor, the thermal element is connected in series with the stator winding of the motor, the normally closed contact of the thermal relay is connected in series in the control circuit of the electromagnetic coil of the AC contactor Adjust the setting current adjustment knob to make the herringbone lever and the push rod an appropriate distance away. When the motor is working normally, the current through the heat element is the rated current of the motor. The heat element heats up, and the bimetal is bent after being heated, so that the push rod is just in contact with the herringbone lever, but cannot push the herringbone lever. The normally closed contact is in a closed state, the AC contactor remains closed, and the motor runs normally.
The working principle of the thermal relay in the motor: If the motor is overloaded, the current in the winding increases, and the current in the thermal relay element increases the temperature of the bimetallic plate higher, the degree of bending increases, and the chevron lever is pushed. The zigzag lever pushes the normally closed contact, disconnects the contact and disconnects the AC contactor coil circuit, so that the contactor releases and cuts off the power of the motor, and the motor is stopped and protected.
The working principle of the thermal relay in the motor: In the actual operation of the motor, such as when the production machinery is dragged to work, if the machinery is abnormal or the circuit is abnormal, the motor encounters an overload, the motor speed decreases and the current in the winding will increase Large, so that the winding temperature of the motor increases. If the overload current is not large and the overload time is short, the motor winding does not exceed the allowable temperature rise, this overload is allowed. However, if the overload time is long and the overload current is large, the temperature rise of the motor winding will exceed the allowable value, aging the motor winding, shortening the service life of the motor, and even burning the motor winding in severe cases. Therefore, this type of overload cannot be sustained by the motor. The thermal relay is the use of the thermal effect principle of current to cut off the motor circuit when there is an overload that the motor cannot withstand, and provides a protective electrical appliance for the motor to protect against overload.
The working principle of the thermal relay in the motor: When the thermal relay is used for overload protection of the motor, the thermal element is connected in series with the stator winding of the motor, the normally closed contact of the thermal relay is connected in series in the control circuit of the electromagnetic coil of the AC contactor Adjust the setting current adjustment knob to make the herringbone lever and the push rod an appropriate distance away. When the motor is working normally, the current through the heat element is the rated current of the motor. The heat element heats up, and the bimetal is bent after being heated, so that the push rod is just in contact with the herringbone lever, but cannot push the herringbone lever. The normally closed contact is in a closed state, the AC contactor remains closed, and the motor runs normally.
The working principle of the thermal relay in the motor: If the motor is overloaded, the current in the winding increases, and the current in the thermal relay element increases the temperature of the bimetallic plate higher, the degree of bending increases, and the chevron lever is pushed. The zigzag lever pushes the normally closed contact, disconnects the contact and disconnects the AC contactor coil circuit, so that the contactor releases and cuts off the power of the motor, and the motor is stopped and protected.
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